328 VETERINARY PHYSIOLOGY 



All these facts seem to indicate that bile is the medium 

 by ivhich the waste products of hepatic metaholism are 

 eliminated, just as the waste products of the body generally 

 are eliminated in the urine by the kidneys. (The action of 

 the liver in general metabolism is considered on p. 353.) 



C Secretion of the Intestinal Wall. 

 (Succus Entericus). 



1. Method of Procuring. — This is formed in the Lieber- 

 kiihn's follicles of the intestine, and it may be procured by 

 cutting the intestine across at two points, bringing each end 

 of the intermediate piece to the surface, and connecting 

 together the ends from which this piece has been taken 

 aAvay, so as to restore the continuous ttibe of the intestine. 



2. Characters. — On mechanically irritating the mucous 

 membrane, a pale, yellow, clear fluid is secreted, which 

 contains native proteins and mucin, and is alkaline in re- 

 action from the presence of sodium carbonate. 



3. Action. — The succus entericus contains : — (1) An 

 enzyme or enz3anes which split some disaccharids, as 

 maltose and cane sugar, into monosaccharids, but do not 

 seem to act on lactose, A special lactase seems to be 

 present in the intestine of young animals taking milk. (2) 

 Lipase is also present. (3) Erepsin, an enzyme which seems 

 to act more powerfully than trypsin in splitting peptones 

 into their component non-protein crystalline constituents, 

 the polypeptides and amino-acids, (4) Enterokinase — a 

 zymin which, acting on trypsinogen, converts it into active 

 trypsin (p. 321). 



4 Mechanism of Secretion Tlie taking of food leads to a 



flow of intestinal secretion wliich reaches its maximum in 

 about three hours ; and this flow is much greater from the 

 upper part of the bowel than from the lower. There is 

 some evidence that the injection of secretin calls forth this 

 secretion, and, according to some observers, the injection of 

 succus entericus into the circulation acts in the same way. 



